1. Field of the Invention
The present invention relates to a retracting mechanism of a zoom lens barrel.
2. Description of the Related Art
A zoom lens system including a first lens group, a second lens group and a third lens group in that order from the object side, wherein the first lens group and the third lens group are integrally moved along an optical axis during a variation of a focal length, is known in the art. A retractable zoom lens barrel including such a type of zoom lens system, wherein a integral movement relationship between the first lens group and the third lens group is canceled to bring the first lens group close to the second and third lens groups to reduce the length of the zoom lens barrel when it is retracted to a retracted position (full-retracted position or a power-off position), is also known in the art. In general, a compression coil spring for biasing the second lens group and the third lens group in opposite directions away from each other is installed therebetween so that the third lens group is moved rearward to its rear moving limit relative to the first lens group by the spring force of the compression coil spring to establish the aforementioned integral movement relationship between the first lens group and the third lens group when the focal length of the zoom lens system is varied (when the zoom lens barrel is in a ready-to-photograph state), and so that the third lens group is brought close to the second lens group (and the first lens group) by compressing the compression coil spring when the zoom lens barrel is retracted to the retracted position.
Such a conventional zoom lens barrel is usually provided with a moving ring which supports the third lens group and is guided along the optical axis of the zoom lens system, and is further provided between the moving ring and another element of the zoom lens barrel with a linear guide mechanism for guiding the moving ring linearly along the optical axis. If an excessive load is applied to the moving ring, an engagement of the moving ring with the another element of the zoom lens barrel through the linear guide mechanism is disengaged, which may cause the moving ring from coming off the zoom lens barrel.
A solution to this problem is to increase the strength of the linear guide mechanism by forming the linear guide mechanism so as to have a complicated structure. However, if the linear guide mechanism is complicated, it will be difficult to install the movable ring into the zoom lens barrel during assembly.